The present invention relates to an adaptive pseudo halftone generator for convering input video signals representative of binary images and images with continuous tones to pseudo halftones.
Pseudo representation of continuous tones may be implemented by a pattern of dots as has been extensively practiced in the graphic art. Applied to photographs and like images consisting of continuous tones, the dot pattern representation satisfactorily reproduces the gray scales or gradations without no false contours developed and, thereby, allows the resulting images to appear natural to the human eye. However, when it comes to alphanumeric characters and other line images which themselves are two-level or binary video image data, the dot pattern representation causes the lines to broaden at the center of a dot pattern and omitted at the periphery, resulting in poor resolution. The resolution may even be so poor that characters are illegible when they are small. While video image data may be digitized using a fixed threshold value in an attempt to preserve the contours of characters and other lines and, thereby, enhance the resolution, such will prevent gradations to be rendered in those parts of video image data which contain continous tones such as photographs, while allowing false contours to appear in reproduced images. Furthermore, the fixed theshold scheme is apt to give unnatural and coarse appearance to resulting images.